If you haven't already, you might try the following;
it's worked at my company without a hitch (as long as the
server is stable). On the server, have one network
connection for the DSL/T1/ISDN/whatever, and another for
the local network. Make sure the internet connection has
its own IP address that is different from the one used on
the local network. (DHCP also works.) Share the one
that connects to the rest of the network using a static
IP and have the clients use that as their default
gateway, telling the computers to connect to the internet
through the LAN.
I hope this helps.
--Dane
